Currently, monovalent ion (e.g., sodium, potassium, lithium and cesium ions) bearing radioactive contaminated, liquid waste (i.e., sodium-bearing nuclear waste) is stored in high level, nuclear waste storage tanks. Under the current Resource Conservation and Recovery Act (RCRA) Land Disposal Restriction (LDR) regulations, this sodium-bearing nuclear waste must be processed with the best demonstrated available technology (BDAT) prior to land disposal. In addition, the current storage tanks do not meet new seismic codes and none of these tanks meet RCRA requirements for secondary containment. As a result, federal and state regulatory agencies now require that the sodium-bearing nuclear waste be depleted from the current storage tank farm pillar and panel tanks by the year 2009 and the remainder of the tanks by 2015.
At this time, the most effective method known for processing the sodium-bearing nuclear waste consists of calcining it as a blend with fluorinel waste generated from fuel reprocessing operations. However, with the curtailment of fuel reprocessing operations at nuclear sites throughout the country, fluorinel waste will no longer be generated. Hence, once radioactive fluorinel waste inventories are depleted, an alternative sodium-bearing nuclear waste processing technology will be required for the remaining waste and all future wastes generated from decontamination activities.
Sodium-bearing nuclear waste cannot be calcined by itself due to the low melting points of sodium and potassium salts relative to the regulated waste calcination temperature. Unless sodium and potassium are minor calcine constituents, the respective melting salts will cause particle agglomerations, which can severely hinder bed fluidization and eventual retrieval of the calcine from the storage bins when the calcine is to be immobilized.
Development efforts have shown that sodium can be acceptably calcined when blended with large amounts of non-radioactive aluminum nitrate. Although the sodium-bearing nuclear waste can be processed with a blend of cold aluminum nitrate, the addition of copious amounts of aluminum nitrate is unattractive due to the increased solid radioactive waste volume and therefore increased costs for calcining, interim calcine storage, calcine immobilization, and disposal in a repository.
Therefore, development efforts are needed to qualify cost effective methods for processing sodium-bearing nuclear waste into a final low-volume waste form. Complicating sodium-bearing nuclear waste treatment is the fact that extensive decontamination activities are planned by various waste sites around the country and current decontamination methods involve large quantities of sodium compounds. As such, to justly address sodium-bearing nuclear waste remediation, alternative decontamination technologies are highly desirable.
Any separation process for removing monovalent ions from sodium-bearing nuclear waste should preferably remove approximately 90% or more of the sodium content from the bulk solution. The present inventors have developed a novel low cost membrane process which combines a separation technique with a substantial cost reduction which satisfies the problems identified above regarding the separation of monovalent ions from radioactive nuclear waste containing such ions.
Sodium-bearing nuclear waste which contain acid sodium solutions are generally the result of decontamination activities at nuclear storage facilities. The sodium content of the sodium-bearing nuclear waste requires dilution if the sodium-bearing nuclear waste is to be vitrified or calcined (i.e., immobilized). Current treatment alternatives remove the radionuclides and toxic metals from the bulk of the waste requiring high level waste disposition. However, these metals provide for good glass formulations; on the other hand, alkali-metals (e.g., sodium, potassium, lithium, cesium, etc.) inhibit such glass formulation. Instead of radionuclide removal, the present inventor's have developed a separation process utilizing membrane electrodialysis and/or diffusion dialysis which subsequently isolate cesium from the alkali-metals using resins. Moreover, if economic incentives exist for commercial use of cesium, then it could be recovered. Otherwise, the cesium impregnated resin can be used as a necessary additive in the glass formulation.
The novel separation process according to the present invention will substantially impact the economic feasibility of radioactive waste disposal by providing a treatment process that will significantly improve the economics and reduce the cost and the volume of immobilization of the liquid nuclear waste which has had its sodium ion content reduced by approximately 90% or more. Implementation of this treatment process will facilitate an efficient environmentally safe solution to the problem of currently stored liquid nuclear waste.
Moreover, this membrane treatment system is capable of separating species into concentrated product streams, withstanding a radiolytic environment, scaling up to processing rates of 2 to 300 gallons (7.57 to 1135.62 liters) per minute, and simple to construct and operate.
The present invention also provides many additional advantages which shall become apparent as described below.